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<title>Local Labels (Using the GNU Compiler Collection (GCC))</title>

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<div class="section-level-extent" id="Local-Labels">
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<h3 class="section" id="Locally-Declared-Labels"><span>6.2 Locally Declared Labels<a class="copiable-link" href="#Locally-Declared-Labels"> &para;</a></span></h3>
<a class="index-entry-id" id="index-local-labels"></a>
<a class="index-entry-id" id="index-macros_002c-local-labels"></a>

<p>GCC allows you to declare <em class="dfn">local labels</em> in any nested block
scope.  A local label is just like an ordinary label, but you can
only reference it (with a <code class="code">goto</code> statement, or by taking its
address) within the block in which it is declared.
</p>
<p>A local label declaration looks like this:
</p>
<div class="example smallexample">
<pre class="example-preformatted">__label__ <var class="var">label</var>;
</pre></div>

<p>or
</p>
<div class="example smallexample">
<pre class="example-preformatted">__label__ <var class="var">label1</var>, <var class="var">label2</var>, /* <span class="r">...</span> */;
</pre></div>

<p>Local label declarations must come at the beginning of the block,
before any ordinary declarations or statements.
</p>
<p>The label declaration defines the label <em class="emph">name</em>, but does not define
the label itself.  You must do this in the usual way, with
<code class="code"><var class="var">label</var>:</code>, within the statements of the statement expression.
</p>
<p>The local label feature is useful for complex macros.  If a macro
contains nested loops, a <code class="code">goto</code> can be useful for breaking out of
them.  However, an ordinary label whose scope is the whole function
cannot be used: if the macro can be expanded several times in one
function, the label is multiply defined in that function.  A
local label avoids this problem.  For example:
</p>
<div class="example smallexample">
<pre class="example-preformatted">#define SEARCH(value, array, target)              \
do {                                              \
  __label__ found;                                \
  typeof (target) _SEARCH_target = (target);      \
  typeof (*(array)) *_SEARCH_array = (array);     \
  int i, j;                                       \
  int value;                                      \
  for (i = 0; i &lt; max; i++)                       \
    for (j = 0; j &lt; max; j++)                     \
      if (_SEARCH_array[i][j] == _SEARCH_target)  \
        { (value) = i; goto found; }              \
  (value) = -1;                                   \
 found:;                                          \
} while (0)
</pre></div>

<p>This could also be written using a statement expression:
</p>
<div class="example smallexample">
<pre class="example-preformatted">#define SEARCH(array, target)                     \
({                                                \
  __label__ found;                                \
  typeof (target) _SEARCH_target = (target);      \
  typeof (*(array)) *_SEARCH_array = (array);     \
  int i, j;                                       \
  int value;                                      \
  for (i = 0; i &lt; max; i++)                       \
    for (j = 0; j &lt; max; j++)                     \
      if (_SEARCH_array[i][j] == _SEARCH_target)  \
        { value = i; goto found; }                \
  value = -1;                                     \
 found:                                           \
  value;                                          \
})
</pre></div>

<p>Local label declarations also make the labels they declare visible to
nested functions, if there are any.  See <a class="xref" href="Nested-Functions.html">Nested Functions</a>, for details.
</p>
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